1. Field of the Invention The invention relates to a bone screw which can be anchored in the bone in a firm and vacuum-tight manner, and to the use of the same in a method of applying bone cement and as a drug delivery system.
2. Description of the Prior Art
In arthroplastic surgery, most implants are inserted in the bony bed using so-called bone cement. This bone cement is usually made of polymethylmethacrylate or related compounds. However, the bone cement can only penetrate into the honeycombs of the bone marrow if they are clean and free of fat marrow and cell components.
In the prior art one therefore attempted to wash the bony bed and apply the bone cement under pressure. This technique, also called the "bone lavage and high-pressurizing technique", was usually used when applying bone cement of a low viscosity.
This technique, however, led to a number of incidents which ended fatally. Studies on animals and clinical examinations both showed that an increase in intramedullary pressure can lead to reflex cardiac arrest and that it is also possible for fatal fat and bone marrow emboli to occur. Furthermore, this method did not succeed in keeping the bony bed free of blood. On the contrary, depending on the blood pressure, the blood flowed into the bony bed and mingled with the bone cement, thus greatly impairing its qualities; this happened every time the intramedullary pressure (IMP) dropped below the blood pressure level.
Attempts have also been made to improve the bone cement used in clinics via mechanical stabilization and prepressurization. This improvement can only be completely successful in the technique of cementing if the achieved material stabilization in the bone cement can be transferred to the bony bed of the patient without endangering his life.